The invention relates to an air mattress capable of remedying, preventing, or relieving bedsores of a patient.
Patients in long term treatments, especially bedridden old patients, are liable to suffer from bedsores. A bedsore is caused by necrosis resulting from venous congestion due to a pressure or patient""s weight acting on the patient""s afferent veins more than the bloodstream blockage pressure.
An air mattress having a lower air pressure in air cells than the bloodstream blockage pressure in afferent veins to prevent bedsores is disclosed in JP-A-7-51325.
This prior art air mattress has a generally rectangular form like a bed, as shown in FIG. 1. The air mattress includes a first bag-shaped body 1 made of a flexible sheet, which in turn included therein a second bag-shaped body 2 made of a flexible sheet and having a smaller surface area than the first bag-shaped body 1. The second bag-shaped body 2 is welded to the inside of the first bag-shaped body 1 at spots A, and at the same time the opposite sides of the second bag-shaped body 2 itself are welded together at multiple weld spots B. The weld spots A at which the second bag-shaped body 2 are welded to the first bag-shaped body 1 are spaced apart in the longitudinal and transverse directions of the bag-shaped bodies at regular intervals, while each of the weld spots B is provided between two longitudinally neighboring weld spots A.
The cross section of the air mattress taken along line Xxe2x80x94X passing through weld spots A and B has a complex sinusoidal structure as shown in FIG. 2. The cross section of the air mattress taken along line Yxe2x80x94Y passing between weld spots A and B has a weakly waving sinusoidal structure as shown in FIG. 3. In this air mattress, the first bag-shaped body 1 has an air pressure not exceeding the bloodstream blockage pressure, which is about 32 mmHg in veins. The pressure in the second bag-shaped body 2 is in the range of 0-30 mmHg. In FIG. 1, reference numeral 3 indicates minute holes formed in the weld spot A to allow the air in the second bag-shaped body 2 to escape. Numerals 4a and 4b refer to air-supply pipes.
The prior art air mattress as mentioned above has the following drawbacks.
(i) Since the weld spots A of the first bag-shaped body 1 and the weld spots B of the second bag-shaped body 2 are aligned along longitudinal lines, each region of the bag-shaped bodies 1 and 2 between two neighboring longitudinal lines forms a slightly waving linear protrusion or crest, as shown in FIG. 3. Such elongate protrusion or crest will have a relatively large tension T in the longitudinal direction when the elongate protrusion is deformed by the weight of a patient 4, as shown in FIG. 4. The tension T reacts on that part of the patient""s skin deforming the protrusion and causes a bedsore. Especially, a portion of the patient""s body where bones e.g. sacrum protrude receives a larger pressure due to the tension T, which can easily cause a bedsore or worsen it.
(ii) Portions of the first bag-shaped body 1 between weld spots As and Bs have a relatively flat top face as shown in FIG. 5, which face tends to creep in Z-direction, thereby posing the same problem as in (i). In particular, the horizontal surfaces of those portions of the first bag-shaped body 1 that correspond to the weld spots B is presumed to be platter in Z-direction than in other directions.
(iii) At the weld spots A, the air mattress has only a single air cell layer of the second bag-shaped body 2, which has an extremely low inner pressure in the range of 0-30 mmHg. As a result, the mattress may develop a so-called bottoming phenomenon in which the portion of the patient""s body lying on the low-pressure section of the mattress sinks to the floor by the weight of the patient, which can be a direct cause of bedsore. The bottoming phenomenon is also a source of uneasiness and uncomfortability for a patient.
It is therefore an object of the invention to provide a low-pressure air mattress which is capable of preventing, remedying, or relieving bedsores of a patient. The inventive air mattress is also capable of preventing bottoming thereof.
In accordance with one aspect of the invention, there is provided an air mattress, comprising:
a first through a fourth flexible sheets which are stacked in the order mentioned and bonded together along the peripheries thereof so as to be sealed together, wherein
the first and second sheets are bonded together at a multiplicity of first bonding spots thereof spaced apart along longitudinal and transverse lines at regular intervals such that four neighboring bonding spots occupy four corners of a tetragon;
the second and the third sheets are bonded together at a multiplicity of second bonding spots thereof at locations which correspond to the centers of the tetragons; and
the third and the fourth sheets are bonded together at a multiplicity of third bonding spots thereof at positions which correspond to the multiplicity of first bonding spots, and wherein
the first and second sheets together define first air cell, the second and third sheets together define second air cell, and the third and fourth sheets together define third air cell.
In this air mattress, tetragonal regions each defined by four neighboring first bonding spots form first protrusions of the first air cell when inflated with air. These first protrusions extend contiguously in the longitudinal and transverse directions. The third air cell has the same structure as the first one when it is inflated. In the second air cell, tetragonal regions each defined by four neighboring second bonding spots form second protrusions extending contiguously in the longitudinal and transverse directions. The apexes of the second protrusions correspond to the first bonding spots.
The tetragons may be squares or rectangles. In this arrangement, both the first and second protrusions each have a semispherical or an oblong semispherical shape, which extend in the two perpendicular directions at regular intervals, thereby creating by the first protrusions substantially isotropic supportive forces to a patient.
It is noted that the first air cell is provided above the second and the third air cells, and that the first and second air cells maintain a sufficiently low air pressure which is less likely to cause bedsores, while the third air cell maintain a high air pressure which is less likely to allow bottoming. In this arrangement, the air mattress may support broad areas of the patient by the multiplicity of supportive soft protrusions of the first and second air cells while preventing bottoming of the air mattress by the third air cell.
The first and the second air cells may be alternately inflated and deflated by air while keeping the third air cell inflated at a predetermined air pressure. In this instance, the air mattress periodically changes supporting areas for the patient to avoid bearing or stressing him at the same physical portions for a long time.
In accordance with the invention, a low-pressure air mattress is provided which have a triple vertical layers of air cells, with the first and second air cells forming two upper layers to maintain a low air pressure to thereby prevent bedsores of a patient and the third air cell forming the lowest layer to maintain a high air pressure to thereby preventing bottoming. It is noted that the high-pressure third air cell serves to prevent bottoming of the air mattress, and that the first and second air cells have a sufficiently low air pressure to prevent bedsores.
In accordance with the invention, each of the first protrusions formed on the surface of the first air cell has a generally semi-spherical shape. Thus, it can be laterally offset only a little when in touch with the skin of the patient and the lateral pull of the skin by the offset is substantially the same in any lateral direction. The invention may prevents a fairly large lateral pull of the skin by an elongate protrusion as encountered in prior art air cells. Thus, the air mattress of the invention may suppress tensions in the air cell that could otherwise act on weaken skins of the patient and cause bedsores.